As is generally known, turbo-generators for generating three-phase current are powered by steam or gas turbines. As a rule, the rotor of a turbo-generator consists of a solid cylindrical forged body made of steel in which the excitation winding is distributed over individual slots. The rotor turns in the bore of the stator of a generator. The stator consists of a sheet metal body which, in turn, has slots to accommodate the armature winding. The decisive factor in the configuration and construction of such turbo-generators is the cooling technology, since this makes it possible to substantially raise the output. Today's turbo-generators often work with a gaseous coolant and with fans that are arranged on the rotor and that circulate the coolant inside the generator.
European patent application EP 1209802 A2 describes the arrangement of a fan in a turbo-generator with a closed cooling-gas circulation system. The cooling gas enters the axial fan from the end of the machine, undergoes a pressure increase in said fan and is thereby conveyed into the machine parts that are to be cooled. Before the cooling gas flows back into the fan, it is passed through heat exchangers.
Moreover, a few cases of air-cooled generators are known from the state of the art with which the air pressure in the generator interior is markedly raised by means of external compressors that are supplied by an external power system. Swiss patent specification CH 541 890 describes boosting the pressure of a generator in order to raise the generator output, whereby compressed air from the compressor of a gas turbine is fed into the generator housing. The low stationary replenishment volume is determined by the leakage rate of the air in the generator, essentially by the leakage volume at the place where the rotor shaft enters the housing. As a result, the volume output flow brought about by the generator ventilation remains practically unchanged. The higher air density achieved in the generator interior leads to an improvement of the cooling properties and can result in an increase in output while the temperature of the generator components remains constant. As a rule, interfaces to the power plant process-control technology are provided. The disadvantages here are the relatively high complexity and the high costs incurred for the external auxiliary devices, for the power and for the process-control technology. Moreover, such an approach is somewhat malfunction-prone.